On 4/7/06, Paul Howarth <paul@xxxxxxxxxxxx> wrote: > Dan Track wrote: > > On 4/7/06, Stuart Sears <stuart@xxxxxxxxxxx> wrote: > >> -----BEGIN PGP SIGNED MESSAGE----- > >> Hash: SHA1 > >> > >> Dan Track wrote: > >>> On 4/7/06, Paul Howarth <paul@xxxxxxxxxxxx> wrote: > >>>> Dan Track wrote: > >>>>> Hi > >>>>> > >>>>> Simple question, I'm running a command `command`, what I'd like to do > >>>>> is check to see if the response is empty then exit. Does anyone know > >>>>> how I can perform that check? > >>>> Exit if "command" produces no output: > >>>> [ -z "$(command)" ] && exit > >>>> > >>>> Paul. > >>> Hi > >>> > >>> Incidentally. What do you have $() instead of just (). > >> $(command) == `command` > >> > >> otherwise you would be testing the length of the literal string '(command)' > >> > >> this way we are running command and testing the length of its output. > >> > >> Regards > >> > >> Stuart > >> - -- > > > > Hi > > Thanks for that. Although never having used it I thought "(command)" > > meant execute the command in a child shell. I thought the pranthesis > > represented anew shell. I take it I'm definitely wrong. If I am wrong > > then what is the difference between (command)=="" and `command`=="" > > (command) > does indeed mean execute the command in a child shell. > > $(command) > is equivalent to > `command` > and represents the standard output from running command > > "(command)" > is the literal text "(command)" > > "$(command)" is equivalent to > $(command) > but the quotes guard against spaces in the output from running command > being used by the shell to split the output into multiple words, as > [ -z $(command) ] > would likely generate syntax errors if there were spaces in the output > of running command. > > Paul. Thanks for the info. It all makes sense now. Appreciate it. Dan
